1. Field of the Invention
The present invention relates to a control operation for determining a document size.
2. Description of the Related Art
Conventionally, some image forming apparatuses such as digital multifunction peripherals include an auto document feeder (ADF) for automatically feeding documents placed on a sheet feed tray to a reading unit one by one.
FIG. 10 illustrates an ADF of a scanner unit 90 of an image forming apparatus.
The scanner unit 90 feeds documents 99 placed on a document tray 97 one by one, conveys a fed document 99 over a reading unit, and optically reads a document image.
When the scanner unit 90 reads documents in such a way, generally, the scanner unit 90 switches document-image reading sizes by using an optical mechanism. For example, the scanner unit 90 changes the speed at which the document 99 is conveyed over the reading unit, depending on the resolution or magnification. To determine the image reading size of a document, the scanner unit 90 needs to determine the size of the document before starting reading the document 99.
Japanese Patent Application Laid-Open No. 2001-13740 discusses an apparatus including a sensor for detecting the leading and trailing edges of a document along a document conveyance path. This apparatus uses the sensor to determine the length of the document in a sub-scanning direction (the direction illustrated by an arrow 92).
The apparatus discussed in Japanese Patent Application Laid-Open No. 2001-13740 also includes a sensor on a document tray, and this sensor determines the length of the document in a main-scanning direction (the direction illustrated by an arrow 91). Examples of such sensor include a sensor for detecting the width of a document stack guide 98 in FIG. 10.
Japanese Patent Application Laid-Open No. 6-291947 discusses an apparatus requiring a reduced number of sensors for determining the document size. This apparatus does not include a sensor for detecting the document size on a document tray. Instead, after the apparatus determines the length of a document in the sub-scanning direction by using a sensor for detecting the leading and trailing edges of the document, the apparatus uses the determined length to determine the length of the document in the main-scanning direction.
The apparatus discussed in Japanese Patent Application Laid-Open No. 6-291947 requires a reduced number of sensors. However, based on this apparatus, the leading and trailing edges of a conveyed document are detected by a sensor to determine the length of the document in the sub-scanning direction, and the document size is determined based on the determined length. Thus, the apparatus needs to convey the document for determining the document size.